The goal was to analyze the influence of blurring of artificial lesions on observer performance during AFC experiments
in chest CT images. Lesion images were generated by scanning Teflon rods of multiple sizes (3/16", 1/4", 5/16", 3/8",
and 1/2") in a General Electric VCT scanner. Images were reconstructed using Bone and Detail reconstruction
algorithms and cropped for use in AFC experiments. Three sets of artificial lesions (simple disks) were generated
mathematically at the same sizes as the Teflon lesions, with two of the sets blurred with 3x3 and 5x5 averaging kernels.
All lesions were scaled to have the same maximum intensity. Approximately 180 normal chest CT images (both Bone
and Detail algorithm) were collected under IRB exemption for use in 2-AFC experiments. Two observers conducted
AFC experiments using the Teflon lesions with the appropriate CT images, and using the artificial lesions in both sets of
CT images. A performance metric was calculated that allowed comparison of experimental results. For Bone algorithm
images, the Teflon and un-blurred lesions produced equivalent performance. Performance was significantly worse using
the blurred lesions. For the Detail algorithm images, un-blurred lesion performance was significantly better than with the
Teflon lesion. The performance using the 3x3-blurred lesions was the closest to the Teflon lesion performance, though it
was slightly worse. Using these results, it is possible to design artificial lesions of any size for use in AFC experiments
that will result in observer performance equivalent to that when using lesions derived from physical phantoms.